Moisture indicating apparatus



April 24, 1956 R. s. FEIGAL ET AL 2,742,780

MOISTURE INDICATING APPARATUS Filed Oct. 27. 1950 l I 23 i a I -37 I I il I 2e| I s I 25 135 zafl I 38 J L 1 INVENTOR. JERRY .HAGEN RICHARD S.FEIGAL ATTORNEY United States Patent MOISTURE INDICATING APPARATUSRichard S. Feigal and Jerry Hagen, Minneapolis, Minn,

assignors to Minneapolis-Honeywell Regulator Company, Minneapolis,Minn., a corporation of Delaware Application October 27, 1950, SerialNo. 192,488 Claims. (or. 73-73 The present invention is concerned withmoisture indicating apparatus and particularly with that type ofapparatus used where the moisture condition of stored grain is to bemeasured at a plurality of locations throughout the grain.

it is well known that the relative humidity, of the air found in theinterstices of a grain mass bears a definite relation to the moisturecontent of the grain. By experience, it appears that spoilage of thegrain may be expected if the relative humidity of the interstitial airis above about 75%. Because of the difliculty of obtaining properlyrepresentative samples from a large grain mass, it has been proposedthat humidity responsive elements such as described in Dunmore Patent2,285,421, or preferably, in Squier application Serial No. 17,622, filedMarch 29, 1948, now Patent N0. 2,543,384, be distributed about the mass.This arrangement has not been fully satisfactory before this inventionbecause of the capacitance effects of the long leads necessarilyinvolved, the previous solutions to this capacitance problem not beingentirely successful.

It is therefore an object of the present invention to provide animproved moisture indicating apparatus of the type that will give anaccurate indication of the moisture condition of a stored substance.

A further object of the present invention is to provide an improvedmoisture indicating apparatus which will accurately indicate themoisture condition at a plurality of positions throughout a storedsubstance wherein a high impedance moisture responsive element iselectrically coupled to a cable so as to present a low impedance to thecable.

A still further object of the present invention is to provide animproved moisture indicating apparatus that is a permanent installationwithin a storage bin and will protect the plurality of moistureresponsive devices from the abrasive effect of the grain at times suchas when the storage bin is being filled.

Still another object of the present invention is to provide an improvedmoisture indicating apparatus wherein each of the plurality of moistureresponsive devices is inoperative at all times except during a shortinterval necessary to obtain a reading of the moisture condition at theparticular moisture responsive device.

A further object of the present invention is to provide an improvedmoisture indicating apparatus wherein each moisture responsive deviceincludes a high impedance element responsive to moisture and an electrondischarge device fixed in a housing which will protect the impedanceelement from the heat radiated by the electron discharge device duringthe short time interval the electron discharge device is operative.

These and other more detailed and specific objec will be disclosed inthe course of the following specification, reference being had to theaccompanying drawings, of which:

Figure 1 shows a typical installation of the invention in a grainstorage bin;

Figure 2 shows a cutaway view of one of the of moisture responsivedevices, and;

Figure 3 shows the electronic circuit used in the improved moistureindicating apparatus.

Referring to Figure 1, the numeral 1 represents a storage bin of thetype used to store grain. Rigidly fixed in this bin is a platform 2 towhich is attached a supporting conduit 3 along which the housings 4 ofthe moisture responsive devices are spaced at appropiiate intervals, sayfive feet, in the substance 16 being stored. The conduit 3 contains amulti-conductor cable 5 which connects the platform 2 to a junction box6 on the outside of the storage bin wall from which the cable 5 extendsto an indicating device located, for instance, in a building 8. Thiscable 5 should be a good grade of moisture resistant insulated cable theA. C. supply line in the cable being twisted to minimize inductioneffects.

An individual moisture responsive device 20 is shown in Figure 2, withnumeral 21 representing an electron discharge device. The electrondischarge device 21 is separated from the moisture responsive impedanceelement 26 by a wall 11 which is rigidly fixed to the housing plurality4 of the device, the element 26 being of the aforemen-.

tioned Squier or Dunmore type. This figure also shows the conduit 3 andthe shoulder 12 which fixes the housing 4 rigidly to the conduit 3. Theimpedance element 26 may be attached to the housing 4 in any practicalmanner and is shown to be held by two bolts 13. It has been foundpreferable to prevent dust from affecting the element 26 by mounting theelement 26 with the active portion 9 on the under side of the element26. This housing 4 also includes a chamber 14 in which is housed theremainder of the electronic circuit which includes the electrondischarge device 21 and the imped-. ance element 26. The housing 4 iscovered by a wire cloth screen 15 which will allow the moisture in thestored substance to affect the impedance element 26 but will keep thesubstance 16 out of contact with the element 26. This screen 15 willalso prevent any flame or spark which may develop in the housing 4 fromescaping to the surrounding atmosphere. This is an importantconsideration in a grain storage bin where an explosive atmosphere islikely to be encountered.

Referring to Figure 3, three identical moisture responsive devices 20,30 and 40 of the type indicated in Figures 1 and 2, with the housing 4of each indicated by dotted lines, are shown connected by conductors 50,51,

52, 53, 54, 55, and 56 to an indicating device 57 in a housing alsoindicated by dotted lines, The conductors 51, 52, 53, 54, 55, and 56 areshown partially as dotted lines to indicate that they are longconductors such as contained in cable 5, referring to Figures 1 and 2.

The moisture responsive device 20 .includes an electron discharge devicein the form of a triode 21 having an anode 22, a control electrode 23,and a cathode 24 of the directly heated type. A relatively highimpedance element in the form of a resistor 25 is connected in a seriescircuit with a high impedance moisture responsive element 26 of theresistance type. The junction between the resistor 25 and the moistureresponsive element 26 is ductor 50. The power supply 58 is then groundedat .86. The series circuits of the three moisture responsive devices 20,and .40, comprising resistors 25, 35, and ,45 connected in a seriescircuit with resistance elements 26, 36 and 46 respectively, are joinedin parallel by common conductors and by means of conductors and 56 areconnected to the secondary winding 60 of a transformer 59 located in theindicating device 57. This transformer 59 also contains a primarywinding 61 which is connected to an alternating current source of power,not

shown, and a second secondary winding 62 which supplies the filamentvoltage for a filament 63 of an electron discharge device 80. In someinstances, it may be necessary to shield one or both of conductors 55and 56, as indicated by shield 64 which is grounded at 65, to preventinteraction between these conductors and the conductors 50, 51, 52, 53and 54. However, the latter group of conductors need not be shielded.Conductor 56 may also be grounded at the moisture responsive devices 20,30 and 40 as shown at 28, 3S and 48, respectively and at the indicatingdevice 57 as shown at 79.

A conductor 51 connects one terminal of each of the cathodes 24, 34 and44 to a direct current source of power 66 which is also connected to themovable contact arm 67 of a switch 68. The remaining terminal ofcathodes 24, 34, and 44 is connected by conductors 52, 53 and 54,respectively, to the fixed contacts 69, 70 and 71 respectively of switch68. The movable contact arm 67 of switch 68 is connected by conductor 72to a source of variable bias voltage 73 and then to a relatively lowimpedance 74 in the form of a resistor which is connected to ground at75. Resistor 74 is connected in current controlling relation to theelectron discharge device and the output of discharge device 80 containsa meter 81 which is calibrated to indicate the moisture condition at oneof the moisture responsive devices 20, 30 or 40 as selected by switch67.

The indicating device 57 is provided with an on-off switch actuator orhandle, not shown, which will open a switch 82 in conductor 50, open aswitch 84 in the primary winding 61 of the transformer 59, and open theswitch located in the output circuit of electron discharge device 80.The movable contact arm 67 of the switch 68 is provided with a deadfixed contact 83 and the switch is returned to this position when nomeasurement is being made.

Operation of Figure 3 In discussing the operation of the moistureindicating apparatus it will be assumed that an operator wishes todetermine the moisture condition of the stored substance and that theon-oif switch actuator or handle, not shown, of the indicating device 57is at the on position so that switches 82, 84 and 85 are closed. Theoperator then moves the movable contact arm 67 of the switch 68 from thedead contact 83 to the switch contact associated with the moistureresponsive device he wishes to operate, for example to contact 69. Thisenergizes the cathode 24 of'triode 21 located in the moisture responsivedevice 20.

The current flow of the triode 21 can be traced from the positive,terminal of the direct current power source SSthrough switch.82,conductor 50, anode 22, cathode 24, conductor 52, switch contact 69,switch arm 67, conductor 72, bias supply 73, resistor 74, ground 75 toground 86 and back to the direct current power source 58.

The control voltage circuit for triode 21 can be traced from the upperend of the transformer secondary winding 60, through conductor 55, thehumidity responsive element 26, resistor 25, and conductor 56 back tothe secondary transformer winding 60. Moreover, this control voltage isdetermined primarily by the portion of the transformer 59 alternatingcurrent voltage present across the high resistance resistor 25. It canbe seen from this circuit that as the resistance of the humidityresponsive humidity element 26 decreases, as it would for a condition ofhigher humidity, at greater portion of the trans' former 59 voltagewould appear across resistor 25. In this manner the humidity responsiveelement affects the control voltage of triode 21, and the current flowthrough the triode 21 produces a signal voltage, proportional to thehumidity condition at the humidity responsive high resistance element 26at the low resistance resistor 74 located in the indicating device 57.This signal controls the current flow through electron discharge device80 and thereby the indication of meter 81 which then gives a visualindication of the moisture condition at this one location within thestored substance. Meter 81 is of the type which will give an indicationof the alternating component of current in the plate circuit ofdischarge device 80. The adjustable bias device 73 is used as acalibration means for meter 81 and is adjusted so the reading on meter81 corresponds to the measured humidity. Normally this is adjusted uponinstallation of the system and needs no further attention.

If the operator now wishes to obtain an indication of the moisturecondition at the position related to the moisture responsive device30'it is necessary that he move the movable contact arm 67 of switch 68to fixed contact 70. The cathode heating circuit of the moistureresponsive device 30 is now energized and after the short time necessaryfor the cathode 34 of triode 32 to heat to an electron emittingcondition, the meter 81 will indicate the moisture condition at theposition of the moisture responsive device 30. Likewise, moving theswitch arm 67 to fixed contact 71 will allow the operator to obtain anindication of the moisture condition at the posi tion of moistureresponsive device 40.

From the foregoing description it can be seen that a moisture indicatingapparatus has been provided which will indicate the moisture conditionat a plurality of positions remote from the indicating device and willdo so by electrically coupling a high resistance humidity responsiveelement to a low resistance through a relatively long electricalconnection. This electrical coupling is recognized as a cathode followercircuit, which is well known in the art, which is modified by placingthe cathode resistor at a position remotely located from the remainderof the cathode follower circuit, the remainder of the circuit includinga plurality of selectively operable portions. Since a cathode followercircuit has the inherent characteristic of a low output impedance and ahigh input impedance with our invention it is possible to couple a highimpedance moisture responsive element to a long electrical cable suchthat the capacitive characteristics of the cable will not introduce anerror into the apparatus. Further we have provided an apparatus whichprevents the heat generated by the electronic circuit from introducingerrors into the moisture indication.

While we have shown our invention as having three humidity responsivedevices it is feasible to so connect a much larger member into thecircuit, one installation contemplating sensing from differentlocations. It is also understood that the indicating device may compriseavariety of devices other than a meter, giving a visual indication. Itis therefore to be understood that our invention is to be limited solelyby the scope of the appended claims.

We claim:

1. In combination; an electrical power source; switch ing means;indicating means; a plurality of moisture responsive means located at aplurality of positions remote from said indicating means, each of saidmoisture responsive means including a moisture responsive impedanceelement normally arranged to be responsive to the moisture content ofthe air surrounding said impedance element, an electron discharge devicefor each moisture responsive element, each discharge device having ananode, a control electrode and a cathode, and a heat energizing circuitfor each of said cathodes; an anodecathode output circuit for eachdischarge device; circuit means connecting said anode-cathode circuitsof said discharge devices in parallel to said power source; meansconnecting each of said moisture responsive impedance elements to itsrespective control electrode; a source of alternating potential, saidmoisture responsive impedance elements being connected in parallel tosaid source of alternating potential; means connecting said switchingmeans and said heat energizing circuit in a series circuit, saidswitching means having switch contacts for rendering any one of saidplurality of moisture responsive means operative by energizing its heatenergizing circuit and rendering all other of said moisture responsivemeans inoperative by rendering their associated heat energizing circuitsinoperative to thereby prevent the continued heating of the airsurrounding the moisture responsive element associated with each of saidother moisture responsive means; and means including a low impedanceline connecting said cathodes to said indicating means whereby saidmoisture responsive element is coupled to said remote indicating means.

2. Apparatus for measuring the moisture content of a stored substancecomprising: indicating means having a low impedance input; a pluralityof moisture responsive means located at a plurality of positionsthroughout said stored substance; each of said moisture responsive meansincluding an electron discharge device connected to have a. lowimpedance output circuit, a high impedance element responsive tomoisture, and a housing, said housing being constructed so as to shieldsaid impedance element from the heat generated by said electrondischarge device; said electron discharge device having a cathode, saidcathode having resistance whereby said cathode is heated to an electronemitting condition when current is caused to flow through saidresistance; means connecting said high impedance element in currentcontrolling condition to said electron discharge device; switchingmeans; a source of direct current potential, said low impedance outputcircuit comprising the cathode circuit and including means connectingsaid switching means, said direct current source, and said cathoderesistances in a series loop, said switching means having contacts forenergizing any one of said cathode resistances thereby rendering theassociated responsive means operative only when an indication of themoisture at the associated responsive means is desired to therebyprevent the continued heating of said cathode from affecting the mediumsurrounding said moisture responsive element, and means connecting thelow impedance input of said indicating means to the low impedance outputcircuit of said discharge devices of said plurality of moistureresponsive means.

3. Moisture indicating apparatus comprising: current responsiveindicator means; switching means; a source of electric power; aplurality of moisture responsive means located at a plurality ofpositions remote from said previously named elements, each of saidmoisture responsive means including an impedance element responsive tomoisture and responsive to the moisture content of the mediumsurrounding said element, an electron discharge device having electrodesincluding an anode and a cathode, a heating circuit for said cathode,said cathode being heated to an electron emitting condition when currentis caused to flow through said heating circuit, and means connectingsaid moisture responsive impedance element in current controllingrelation to said electron discharge device; an anode-cathode outputcircuit for each discharge device; means connecting the anode-cathodeoutput circuits of said discharge devices to said indicator means incontrolling relation thereto; means including said switching meansconnecting the cathode heating circuits of the electron dischargedevices of said plurality of moisture responsive means to said source ofelectric power, said switching means having a controlling position foreach of said heating circuits for selectively energizing any one of saidcathode heating circuits from said source of power thereby rendering theassociated moisture responsive means operative so that an indication ofthe moisture at the associated moisture responsive means is obtained,said onecircuit being energized only when a moisture indication isdesired, thereby preventing the continued heating of the cathode fromaifecting the medium surrounding said moisture responsive element.

4. Apparatus for measuring the moisture content of a stored substancecomprising in combination: a source of relatively constant alternatingpotential; a resistor; a high impedance resistive element responsive tomoisture; circuit means connecting said resistor and said resistanceelement in circuit with said source of alternating potential, saidcircuit means including a first junction between said resistor and saidsource which is connected to a reference potential point; a source ofpositive potential with respect to the reference potential; anelectronic discharge device having an anode, a control electrode and acathode, and a heating circuit for said cathode, said cathode beingheated to an electron emitting condition when current is caused to flowthrough said heating circuit; means connecting said control electrode toa second junction of said circuit means between said resistor and saidresistance element to provide an alternating signal for controlling saiddischarge device in accordance with the resistance value of saidmoisture responsive impedance; means connecting said anode to saidsource of positive potential; a load resistor; switching means; a sourceof electric power; means including said switching means for connectingsaid cathode heating circuit to said source of power to provide currentflow through said circuit and for connecting one terminal of said loadresistor to said cathode of said electronic discharge device, the otherterminal of said load resistor being connected to said referencepotential point; and indicating means connected to said load resistorand responsive to the current flow through said load resistor.

5. Apparatus for measuring the moisture content of a stored substancecomprising; indicating means having a low impedance input; a pluralityof moisture responsive means located at a plurality of positionsthroughout the substance, each of said responsive means including a highimpedance element, each responsive means also including an electrondischarge device having an anode, a cathode, a control electrode, andheating means for each of said cathodes, a source of direct currentpotential, switching means, means connecting said direct current source,said switching means and said heating means in a series circuit whichcomprises a cathode heating circuit, said switching means havingcontacts for rendering any one of said moisture responsive meansoperative by energizing its cathode heating circuit and rendering allthe other responsive means inoperative by rendering their associatedheating circuits inoperative to thereby prevent continued heating of theinterstitial air surrounding the moisture responsive element associatedwith each of the other moisture responsive means, a low impedance outputcircuit connected to the cathode of each of said discharge devices, eachof said high impedance elements being exposed to the interstitial air inthe stored substance; an anode-cathode output circuit for each electrondischarge device; means connecting the anode-cathode circuits of saiddischarge devices in parallel and to a source of direct potential; meansconnecting said high impedance elements in current controlling relationto the respective electron dis- 7 "8 charge devices, and-meansconnecting the input offsaid 2,367,561 Boyoucos Jan.- 16,1945 indicatingmeans to the low impedance output circuit. 12,367,924 Briggs Jan. 23,1945 e c 2,454,584 Zihgaro Nov. 23,1948 References Cited in the file bfthispatent 2,483,410 Grieg et a1 OCL4, 1-949 UNITED STATES T S 52,522,348 Dahline "Sept. 12, 1950 1,749,826 Lubach M n 11,1930 79162vemimase TT'T. 1951 1,765,816 Allen J uhe24,1 93jO OTHER ER E? M I2015,1515 Polin $PF-" 1. v ,JOurnal of Research of the National Bureauof Stand- 2,252,613 e y f 12,1941 10 ards, p 701-714, vol. 23, December1939. 2,285,421 Dunmore June 9, 1942

